1. Field of the Invention
This invention relates to abrasive tools for grinding, cutting, drilling, and other machining of hard materials. More particularly, this invention relates to carbon bonded abrasive tools and a process for bonding abrasives in a carbon bond.
2. State of the Art
Machinists use abrasive tools for grinding, cutting, drilling, and other machining of hard materials. Examples of such abrasive tools include grinding and cutting wheels and their elements, honing sticks, lapping tools, drills, reamers and others. Abrasive tools are used for both mechanical and electrical discharge machining (EDM).
Present abrasive tools are composed of super abrasive materials such as diamond powder or cubic boron nitride (CBN) powder held in a resin bond. Typical resin bonds include phenol formaldehyde and polyamide. Abrasive tools made of diamond powder are used to machine cemented carbides, semiconductors, ceramics and other hard fragile material. Abrasive tools made of CBN are used to machine nickel-based super alloys, hardened steel alloys, and other metal materials.
There is a continual need for improved abrasive tools suitable for higher rates of production under extremely rigorous work conditions such as cutting, slitting, plunge grinding, super finishing and/or rapid material removal. Operation under such conditions generates excessive heat which causes resin bond abrasive tools to deteriorate rapidly.
There are several reasons for this rapid deterioration of resin bond abrasive tools operating under severe conditions. First, resins have a higher thermal coefficient of linear expansion as compared to the thermal coefficient of linear expansion of abrasives such as diamond and CBN. Under extreme conditions, as the temperature of the tool increases, the expansion of the resin is greater than the expansion of the abrasive. As a result, the resin and the abrasives separate, forming micro cracks throughout the resin bond abrasive tool. This crack formation decreases the strength of the bonding resin and hence, the service life of the tool.
The heat problem is further aggravated by the inherent low thermal conductivity of the resins. As a result, the extremely high temperatures generated in the contact zone between the abrasive instrument and the work piece is not rapidly dissipated. A bonding material with a higher thermal conductivity than that of the resin would more effectively dissipate heat away from the contact zone into cooler areas of the tool, into other machinery, and into lubricants. Therefore, destructive temperatures could be better avoided.
Finally, the resin acts as an electrical insulator, making present resin based abrasive tools unsuitable for electrical discharge machining.